1. Field of the Invention
The present invention is generally related to DC-to-DC power converters and, more particularly, is directed to circuitry for suppressing turn-on current transients of such power converters.
2. Description of the Prior Art
Unsuppressed turn-on current transients of DC-to-DC power converters can cause serious reliability problems in airborne or spacecraft DC power systems. Techniques presently utilized to limit current transients occurring at the initial application of power to a DC-to-DC converter include the placement of large inductors at the input to the converter to limit the rate of rise of the input current. One serious disadvantage of such a large input inductor is the size and weight of a component necessary to perform the job, which becomes particularly acute in high power spacecraft applications and the like. Further, energy stored in such an input inductor must be dissipated when the unit is turned off by means of a damper resistor or diode to prevent large voltage transients. The latter requirement further complicates the necessary circuitry and increases cost.
Another technique presently in use, as exemplified by prior U.S. Pat. No. 3,376,478 to Sheng et al, is known as an active voltage rate of rise circuit which provides a ramp input voltage to the converter circuit. Such circuits, while generally effective, do not guarantee a transient-free input current. This is particularly true in the case of self-oscillating converters with heavy loading wherein regenerative oscillation may not commence until a substantial percentage of the rated input voltage is supplied to the converter. When regenerative oscillation commences, the output capacitance of the converter charges rapidly to cause a current spike at the input terminals. Such a current surge will go unsuppressed in a prior art low impedance ramp voltage follower. That is, it is clear that current surges can exist even when the rate of rise of the input voltage is controlled, as in the prior art patent to Sheng et al. Accordingly, it is seen that a need exists for an effective, reliable and simple circuit for limiting current transients and current rate of rise upon the application of power to a DC-to-DC power converter.